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Disease guideInfection with Marteilioides chungmuensis

What is it?

Infection with Marteilioides chungmuensis, also known as marteilioidosis, is a protozoan parasite of the phylum Paramyxea, and is responsible for infection of Pacific oyster oocytes. M. chungmuensis infects the cytoplasm of mature oocytes and can affect a substantial proportion of eggs. Infected oysters lose their marketability, due to their abnormal appearance.

Where and when might it occur?

Prevalence of infection increases during spawning in summer and decreases after spawning in winter. Prolonged spawning activity of infected oysters has been observed, resulting in nutritional wasting and mortality. Mode of transmission is unknown; however, intermediate hosts may be involved in the life cycle of the disease.


The disease is often identified by spawning failure and high mortalities.

Gross pathological signs are:

  • visible distension of the mantle surface due to infected eggs retained within the follicle
  • nodule-like structures on the gonad surface

Microscopic pathological signs are:

  • parasites within oocytes

Source: Australian Government, Department of Agriculture, Fisheries and Forestry

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